Fibroblast Growth Factor 18 (FGF-18) is a member of the Fibroblast Growth Factor (FGF) family of proteins, closely related to FGF-8 and FGF-17. Members of the FGF family are characterized by heparin binding domains. Such a putative heparin-binding domain has been identified for FGF-18. It is postulated that receptor-mediated signalling is initiated upon binding of FGF ligand complexed with cell-surface heparin sulfate proteoglycans. It has been shown that FGF-18 is a proliferative agent for chondrocytes and osteoblasts (Ellsworth et al., 2002; Shimoaka et al., 2002). FGF-18 has been proposed for the treatment of cartilage disorder such as osteoarthritis (OA) and cartilage injury (CI) either alone (WO2008/023063) or in combination with hyaluronic acid (WO2004/032849).
Pharmaceutical compositions comprising an FGF polypeptide are known in the art. WO2012172072 describes a freeze-dried formulation containing FGF-18, wherein said composition comprises FGF-18, a buffer, a poloxamer surfactant and a sugar as stabilizing agent. Said FGF-18 freeze-dried formulation is showing promising results in the treatment of OA or CI. The current dosing regimen, using said freeze-dried formulation, is a treatment cycle of once weekly injection for 3 weeks. The treatment cycle can be repeated.
The main drawback of the current FGF-18 formulation is that, once injected intraarticularly (i.e.), the presence of FGF-18 in the synovial fluid may also induce uncontrolled cartilage growth in healthy areas. This can induce, of course, unwanted effects such as reduced joint mobility. The delivery of FGF-18 selectively at the level of the target site could promote the cartilage growth only in the damaged area. In particular, the delivery of FGF-18 at the level of the damaged area could be highly beneficial for the treatment of OA or CI, notably when coupled with microfracture. Microfracture is an articular cartilage repair surgical technique that works by creating small fractures in the underlying bone. This causes the release of pluripotent mesenchymal stem cells from the bone marrow (Ringe J. et al., 2012). Filling the cartilage hole with a scaffold or a membrane containing FGF-18 would direct cells within said matrix that would, then, act as mechanical supports for cell growth and drug reservoirs at the same time. For this reason, it would be preferable if FGF-18 is slowly released from the scaffold/membrane to the surrounding tissue and/or stays entrapped in the scaffold/membrane.
A typical approach in tissue engineering is the confinement of growth factors in a 3D matrix, i.e. on a scaffold or membrane, that can be either implanted or injected, depending on its mechanical properties, in order to assume the shape of the acceptor site (Yun et al., 2010). Mandatory characteristics of the scaffolds/membranes are biocompatibility and resorbability. Additionally, scaffolds/membranes must be able to provide cells with the ideal environment to grow, proliferate and reform the damaged tissue. Ideally, the matrix should resemble the same mechanical properties as the original tissue and should present a microporosity able to host cells (interconnected pores with a sufficient size) (Tessmar and Gopferich, 2007).
Some matrices useful for tissue engineering are already commercialized. For instance, Chondro-Gide™ membrane (Geistlich Biomaterials) consists of collagen types I and III, arranged in a bilayer structure. This membrane has been approved in some countries, for instance in France, in combination with autologuous chondrocyte implantation (preferably in combination with the approved product ChondroCelect™). A similar product, Maci (Genzyme), has been recently approved in the European market. It consists of autologous chondrocytes expanded ex vivo expressing chondrocyte-specific marker genes, seeded onto a Type I/III collagen membrane (Maix). Chondromimetic™ (Orthomimetics Ltd.) is a scaffold composed of type I bovine collagen and chondroitin-6-sulphate glycosaminoglycan (collagen/GAG scaffold). This implant has also been approved for the European market.
For instance, WO2012113812 describes nanofibrous scaffold functionalized via coating with polyelectrolyte multilayers, i.e. at least one layer of polyanions and one layer of polycations. Therapeutic molecules, such as FGF-18, can be included in the polyelectrolyte multilayers. In particular, the therapeutic molecule can form the polyanion layer. Said scaffold may optionally further comprising osteoblasts within a collagen hydrogel and chondrocytes within an alginate hydrogel, each hydrogel being deposited on the coated scaffold. Said scaffold is to be implanted in situ, via surgery.
When preparing a pharmaceutical composition comprising a bioactive protein, said composition must be formulated in such a way that the activity of the protein is maintained for an appropriate period of time. A loss in activity/stability of the protein may result from chemical or physical instabilities of the protein notably due to denaturation, aggregation or oxidation. The resulting products may thus be pharmaceutically unacceptable. Although the use of excipient(s) and/or matrix is known to increase the stability of a given protein, the stabilizing effects of these excipients is highly dependent on the polymer in the matrix, the nature of the excipients, if any, and the bioactive protein itself.
Although tissue engineering procedures are promising, integration rate or quality of the cartilage produced has to be improved. There is therefore a need of an improved composition, allowing good integration and good quality of the cartilage produced (i.e. mainly hyaline cartilage); there is also a need for an alternative system to provide a therapeutic compound to the site of defect. Indeed, generation of said hyaline cartilage is valuable both as a therapeutic and as a component for biological matrices (Power et al., 2012). Said compositions could be useful in the frame of tissue engineering procedures for the treatment of a cartilage disorder in a patient, such as osteoarthritis, cartilage injury or osteochondral defects.